1. Technical Field
The present invention relates to a light emitting apparatus, a method for driving the light emitting apparatus and an electronic apparatus.
2. Related Art
In recent years, there have been proposed light emitting apparatuses using a light emitting device such as an organic light emitting diode (hereinafter, referred to as “OLED”) device including those called an organic EL (electroluminescent) device and a light emitting polymer device.
For example, JP-A-2007-310311 discloses a light emitting apparatus using a pixel circuit P0 shown in FIG. 14. As shown in FIG. 14, the pixel circuit P0 includes a driving transistor 3B and an OLED device 3D which are arranged in series with each other, a switching device 3A arranged between a gate of the driving transistor 3B and a data line DTL101, and a capacitive element 3C. As shown in FIG. 14, the OLED device 3D is accompanied by a capacitance 31.
Next, an action of the pixel circuit P0 is described. In a first period, when a potential of the data line DTL101 is set to a reference potential V0, and the switching device 3A is set to be turned on, a gate potential of the driving transistor 3B is reset to the reference potential V0. In a second period, a power potential supplied to a power line DSL101 is set to be a potential Vcc_L much lower than the reference potential V0. The potential Vcc_L is set so that a voltage between the gate and a source of the driving transistor 3B is higher than the threshold voltage of the driving transistor 3B. This makes the driving transistor 3B be turned on, and a source potential of the driving transistor 3B set to be Vcc_L. In a third period, when the power potential supplied to the power line DSL101 is set to be a high potential Vcc_H, the source potential of the driving transistor 3B starts rising, the voltage between the gate and the source of the driving transistor 3B asymptotically comes close to the threshold voltage of the driving transistor 3B. In a fourth period, when the potential of the data line DTL101 is set to be a data potential Vin corresponding to designated gradation for the pixel circuit P0, the driving transistor 3B is turned on, and a current between a drain and the source flows into the capacitance 3I accompanying to the OLED device 3D. Therefore, the source potential of the driving transistor 3B rises, and a mobility compensation action by negative feedback is performed. That is, the voltage between the gate and the source of the driving transistor 3B (voltage between both ends of the capacitive element 3C) is set to a value in which the data potential Vin and properties of the driving transistor 3B (threshold voltage and mobility) are reflected. In a fifth period (light emitting period), when the switching device 3A is set to be turned off, the gate of the driving transistor 3B is made electrically floating. When a current corresponding to the voltage between both ends of the capacitive element 3C flows in the driving transistor 3B, the source potential of the driving transistor 3B rises, and the gate potential of the driving transistor 3B rises in conjunction with the source potential (bootstrap action). The voltage between both ends of the capacitive element 3C is kept to be the value set in the fourth period. Then, when the source potential of the driving transistor 3B exceeds a light emitting threshold value, the OLED device 3D emits light.
Here, a time length t from a starting point of the light emitting period until the OLED device 3D starts emitting light is determined depending on the source potential of the driving transistor 3B at the starting point of the light emitting period and the current flowing in the driving transistor 3B. More specifically, assuming a difference between the source potential of the driving transistor 3B at the starting point of the light emitting period and the source potential of the driving transistor 3B when the OLED device 3D starts emitting light is ΔVb, the current flowing in the driving transistor 3B is Idata, and a capacitance value of the capacitive element 3I is Coled, the above-described time length t can be represented by formula (I) shown below.t=(Coled×ΔVb)/Idata  (1)
In JP-A-2007-310311 described above, the current Idata flowing in the driving transistor 3B can be set to a value independent of the properties of the driving transistor (threshold voltage and mobility) by the compensation action in the period previous to the light emitting period. However, the source potential of the driving transistor 3B is made to be a value corresponding to the properties of the driving transistor 3B, and the value is difficult to accurately grasp. Unless the source potential value of a driving transistor TDR at the starting point of the light emitting period can be accurately grasped, AVb in the above formula (1) cannot be accurately grasped, and it is difficult to set highly precisely the time length t from the starting point of the light emitting period until the OLED device 3D starts emitting light. Gradation of a pixel recognized by an observer is obtained by integrating a light emission luminance of the OLED device 3D by time in a period while the OLED device 3D actually emits light. However, if the above time length t cannot be set highly precisely, the time length while the OLED device 3D actually emits light in the light emitting period cannot highly precisely be set and the time integral value of the light emission luminance of the OLED device 3D is difficult to set highly precisely. This disadvantageously has made it difficult to set the gradation of the pixel recognized by the observer to a desired value.